Atomic layer deposition of rhenium containing thin films

ABSTRACT

Methods for depositing rhenium-containing thin films are provided. In some embodiments metallic rhenium-containing thin films are deposited. In some embodiments rhenium sulfide thin films are deposited. In some embodiments films comprising rhenium nitride are deposited. The rhenium-containing thin films may be deposited by cyclic vapor deposition processes, for example using rhenium halide precursors. The rhenium-containing thin films may find use, for example, as 2D materials.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/835,849, filed Mar. 31, 2020, which is a continuation of U.S.application Ser. No. 15/827,988, filed Nov. 30, 2017, now U.S. Pat. No.10,619,242, which claims priority to U.S. Application Nos. 62/429,527,filed Dec. 2, 2016; 62/448,211, filed Jan. 19, 2017; and 62/516,282,filed Jun. 7, 2017, each of which is hereby incorporated by reference.

BACKGROUND Field of the Invention

The present application relates generally to atomic layer depositionmethods for forming rhenium-containing thin films, such as metallicrhenium and rhenium disulfide.

Background

Rhenium thin films find use in a wide variety of different applications.For example, metallic rhenium films may be use in catalysis, inhigh-temperature superalloys, in superconducting applications and inmicroelectronics applications. Rhenium disulfide, in contrast, has beenshown to behave similarly to 2D materials, even in 3D bulk form. Thus,rhenium disulfide may find applications in tribology, other low-frictionapplications, solar cell applications and quantum computing andultrafast data processing.

SUMMARY

Rhenium-containing thin films can be deposited by vapor-depositionprocesses, such as atomic layer deposition (ALD) or sequential or pulsedchemical vapor deposition (CVD) processes. In some embodiments metallicrhenium-containing thin films are deposited. In some embodiments rheniumsulfide thin films are deposited. In some embodiments films comprisingrhenium nitride are deposited. The rhenium-containing thin films may bedeposited by cyclic vapor deposition processes, for example usingrhenium halide precursors. The rhenium-containing thin films may finduse, for example, as 2D materials, as channel materials in a logicdevice, as a work function metal in a gate stack, as a copper cappinglayer or as a contact metal layer.

In accordance with one aspect, methods for depositing thin filmscomprising rhenium on a substrate are provided. The methods may compriseone or more deposition cycles each comprising alternately andsequentially contacting the substrate in a reaction space with avapor-phase rhenium precursor and a vapor-phase second reactant. In someembodiments two or more deposition cycles are carried out sequentially.The methods may be atomic layer deposition or pulsed or sequentialchemical vapor deposition methods.

In some embodiments the thin film that is deposited comprises elementalrhenium or rhenium nitride (ReN_(x)). In some embodiments the thin filmcomprises both elemental rhenium and rhenium nitride. However, in someembodiments the thin film does not comprise rhenium nitride. In someembodiments the thin film comprises less than 20 at-% H and less than 5at-% C as impurities. In some embodiments the thin film is deposited ona three-dimensional structure with a step coverage of greater than 90%.

In some embodiments the rhenium precursor is a rhenium halide, such asReCl₅ or ReF₆. In some embodiments the second reactant comprisesnitrogen, and may comprise, for example, NH₃ N₂, NO₂ or N₂H₄. In someembodiments the second reactant is a plasma reactant. For example thesecond reactant may comprise a plasma generated in a reactant gas suchas H₂ and/or a noble gas. In some embodiments the second reactant doesnot comprise oxygen.

In some embodiments, the deposition cycles are carried out at adeposition temperature of about 100 to 600° C. or about 250 to about500° C.

In some embodiments the thin film is a metallic rhenium thin film havinga resistivity of about 10 to 500 microOhmcm.

In accordance with another aspect, cyclic vapor deposition methods fordepositing a rhenium-containing thin film on a substrate in a reactionchamber are provided. One or more deposition cycles comprise contactingthe substrate with a first vapor-phase rhenium precursor and a secondvapor-phase reactant. In some embodiments the methods are atomic layerdeposition methods in which the substrate is alternately andsequentially contacted with the first vapor-phase rhenium precursor andthe second reactant. The excess precursor or reactant may be removedfrom the reaction space, along with any reaction byproducts, between thecontacting steps. In some embodiments two or more sequential depositioncycles are carried out until a rhenium-containing thin film of a desiredthickness has been deposited on the substrate. In some embodiments therhenium-containing thin film comprises metallic rhenium, rheniumnitride, rhenium sulfide, rhenium oxide or mixtures thereof.

In some embodiments the methods are atomic layer deposition methods, orsequential or pulsed chemical vapor deposition methods.

In some embodiments the methods are carried out at a depositiontemperature of about 250 to about 500° C. The vapor-phase rheniumprecursor may comprise, for example, a rhenium halide such as ReCl₅ orReF₆. In some embodiments the second reactant comprises one or morereactive species formed by generating a plasma in a reactant gas, suchas H₂ or a combination of H₂ and a noble gas.

In some embodiments the rhenium-containing thin film is a rheniumsulfide film, such as ReS₂, and the second reactant comprises sulfur. Insome embodiments the sulfur precursor comprises hydrogen and sulfur. Insome embodiments the sulfur precursor is an alkylsulfur compound. Insome embodiments the second reactant comprises one or more of elementalsulfur, H₂S, (CH₃)₂S, (NH₄)₂S, ((CH₃)₂SO), and H₂S₂. In some embodimentsthe rhenium sulfide thin film is a two-dimensional material. In someembodiments the rhenium sulfide thin film may serve as a high mobilitychannel material in a logic device.

In some embodiment, the rhenium sulfide thin film has a thickness ofless than about 10 nm, or even less than about 5 nm. In some embodimentsthe deposition cycle is repeated sequentially to form 20 molecularlayers of ReS₂ or less, or 10 molecular layers of ReS₂ or less. In someembodiments less than about 3 molecular layers of ReS₂ are deposited.

In some embodiments, rhenium sulfide is deposited at a growth rate offrom 0.2 to 1 angstrom/s.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram generally illustrating processes fordepositing a metallic rhenium film by ALD.

FIG. 2 is a process flow diagram generally illustrating processes fordepositing rhenium disulfide films by ALD.

FIG. 3 shows GIXRD patterns of metallic rhenium films grown atdeposition temperatures between 150 and 500° C. on Si substrates. Atotal of 1000 cycles were applied.

FIG. 4 shows FESEM images of metallic rhenium films grown at depositiontemperatures between 300 and 500° C. on Si substrates. A total of 1000cycles were applied.

FIG. 5 shows FESEM images of metallic rhenium films grown at depositiontemperatures between 300 and 400° C. on Si substrates. A total of 100cycles were applied.

FIG. 6 illustrates growth rates of rhenium films as a function ofdeposition temperature. 1000 cycles were applied in each deposition.

FIG. 7 illustrates the growth rate of rhenium thin films on Al₂O₃ at400° C. as a function of ReCl₅ pulse length.

FIG. 8 illustrates the growth rate of rhenium thin films on Al₂O₃ at400° C. as a function of NH₃ pulse length.

FIG. 9 illustrates the growth rate of rhenium thin films grown on Al₂O₃at 400° C. as a function of NH₃ flow rate.

FIG. 10 illustrates film thickness of rhenium thin films grown on Al₂O₃at 400° C.

FIG. 11 illustrates the growth rate of rhenium thin films grown on Al₂O₃as a function of deposition temperature.

FIG. 12 illustrates the growth rates (squares) and resistivities(circles) of rhenium thin films grown on Al₂O₃ films at 400° C. as afunction of ReCl₅ pulse length.

FIG. 13 illustrates growth rates (squares) and resistivities (circles)of rhenium-containing thin films grown on Al₂O₃ at 400° C. as a functionof NH₃ pulse length.

FIG. 14 illustrates growth rates (squares) and resistivities (circles)of rhenium thin films grown on Al₂O₃ at 400° C. as a function of NH₃flow rate.

FIG. 15 illustrates the thickness (squares) and resistivities (circles)of rhenium thin films grown on Al₂O₃ from ReCl₅ and NH₃ at 400° C. as afunction of the number of deposition cycles.

FIG. 16 shows GIXRD patterns for rhenium thin films grown on Al₂O₃ at400° C. from ReCl₅ and NH₃ as a function of number of deposition cycles.

FIG. 17 shows FSEM images of rhenium films grown on Al₂O₃ at 400° C.from ReCl₅ and NH₃ at various numbers of deposition cycles.

FIG. 18 shows the growth rates (squares) and resistivities (circles) ofrhenium nitride and rhenium metal films grown on Al₂O₃ as a function ofdeposition temperature.

FIG. 19 shows the GIXRD patterns of the rhenium nitride and rheniummetal films grown on Al₂O₃ as a function of deposition temperature.

FIG. 20 provides the film thickness (EDX) and surface roughness (AFM) ofthe rhenium metal and rhenium nitride films deposited between 250° C.and 500° C.

FIG. 21 provides AFM images (2 micron×2 micron) of the rhenium metal andrhenium nitride films gown on Al₂O₃ as a function of temperature.

FIG. 22 shows FESEM images of rhenium-containing films grown on Al₂O₃ atvarious deposition temperatures.

FIG. 23 provides elemental composition, impurity content andstoichiometry of rhenium-containing films deposited between 250° C. and500° C. as analyzed by TOF-ERDA.

FIG. 24 provides GIXRD patterns of the rhenium sulfide films depositedat temperatures between 150 and 500° C. on Si substrates. A total of1000 cycles were applied.

FIG. 25 provides FESEM images of the rhenium sulfide film deposited at150° C. after change in visual appearance due to contact with a plasticbag surface.

FIG. 26 illustrates growth rates of rhenium sulfide films as a functionof deposition temperature. 1000 cycles were applied in each deposition.

FIG. 27 provides FESEM images of the rhenium sulfide films grown between150 and 500° C. on Si substrates using 1000 cycles.

FIG. 28 shows GIXRD patterns of the rhenium sulfide films grown at 300°C. on native oxide covered Si and ALD-deposited Al₂O₃ surfaces. A totalof 1000 cycles were applied.

FIG. 29 provides FESEM images of the rhenium sulfide films deposited at300° C. on native oxide covered Si and ALD-deposited Al₂O₃ surfacesusing 1000 cycles.

FIG. 30 illustrates the growth rate of rhenium sulfide films on Al₂O₃ at400° C. as a function of ReCl₅ pulse length.

FIG. 31 shows the growth rate of rhenium sulfide films on Al₂O₃ as afunction of H₂S pulse length.

FIG. 32 shows FESM images of the films deposited using various H₂S pulselengths as indicated.

FIG. 33 shows the increasing thickness of rhenium sulfide filmsdeposited on Al₂O₃ at 400° C. using 1 second pulses of ReCl₅ and H₂S,and 1 second purges.

FIG. 34 shows the GXIRD patterns of the rhenium sulfide films depositedon Al₂O₃ at 400° C. with varying numbers of deposition cycles, as inFIG. 33.

FIG. 35 shows FSEM images of the rhenium sulfide films deposited onAl₂O₃ at 400° C. with varying numbers of deposition cycles.

FIG. 36 provides the film thicknesses (d, calculated by EDX) and surfaceroughness (R_(q), calculated by AFM) for the rhenium films depositedwith varying number of deposition cycles.

FIG. 37 shows the growth rate of rhenium sulfide films grown on Al₂O₃films as a function of deposition temperature.

FIG. 38 shows the GXIRD patterns of the rhenium sulfide films depositedas a function of deposition temperature 7.

FIG. 39 shows FSEM images of the films of the rhenium sulfide filmsdeposited as a function of deposition temperature.

FIG. 40 shows the elemental composition, impurity content andstoichiometry of the rhenium sulfide films deposited between 120° C. and500° C. as measured by TOF-ERDA.

FIG. 41 shows the elemental composition, impurity content andstoichiometry of the rhenium sulfide films deposited between 120° C. and500° C. as measured by XPS.

FIG. 42 is an FESEM image of an ALD ReS₂ film.

FIG. 43 is a TEM image of the ALD ReS₂ film of FIG. 42.

FIGS. 44A-D are FSEM images of a rhenium sulfide film deposited in atrench structure.

DETAILED DESCRIPTION

Rhenium-containing thin films can be deposited on a substrate by vaporphase deposition processes, such as atomic layer deposition- (ALD) andchemical vapor deposition (CVD)-type processes. In some embodiments avapor deposition process can deposit a rhenium-containing material, forexample metallic rhenium, rhenium nitride (ReN_(x)), rhenium sulfide,such as rhenium disulfide (ReS₂), rhenium oxide, or mixtures thereof. Insome embodiments the rhenium-containing thin films may comprise rheniumnitride or a mixture of rhenium and ReN_(x). In some embodiments therhenium-containing thin films do not comprise rhenium nitride.

In some embodiments a deposition process uses a first vapor phaserhenium precursor as described herein in combination with a second vaporphase reactant as described herein. In some embodiments the second vaporphase reactant does not comprise oxygen. In some embodiments the secondvapor phase reactant may comprise nitrogen, such as NH₃, or sulfur, suchas H₂S.

In some embodiments vapor deposition processes comprise contacting thesubstrate with a vapor phase rhenium precursor, such as a rheniumhalide, and one or more additional vapor phase reactants. For example,in some embodiments rhenium-containing thin films, such as metallicrhenium thin films, may be deposited by an ALD process comprisingalternately and sequentially contacting a substrate with a vapor phaserhenium precursor, such as a rhenium halide and a second vapor phasereactant. In some embodiments the second reactant does not compriseoxygen. In some embodiments the second reactant may comprise nitrogen,such as NH₃. In some embodiments a rhenium metal film is deposited. Insome embodiments rhenium nitride (ReN_(x)) or a mixture of Re andrhenium nitride may be deposited. In some embodiments rhenium sulfidefilms, such as rhenium disulfide films are deposited. Such films may bedeposited, for example, by an ALD process comprising alternately andsequentially contacting a substrate with a vapor phase rhenium halide,such as ReCl₅ and a vapor phase sulfur-containing reactant, such as H₂S.In some embodiments a rhenium oxide film may be deposited.

Suitable substrate materials on which the rhenium-containing films maybe deposited may include insulating materials, dielectric materials,conductive materials, metallic materials, crystalline materials,epitaxial, heteroepitaxial, and/or single crystal materials such asoxides. For example, the substrate may comprise Al₂O₃, sapphire,silicon, silicon oxide, or an insulating nitride, such as AlN. Further,the substrate material and/or substrate surface may be selected by theskilled artisan to enhance, increase, or maximize two-dimensionalcrystal growth thereon. In some embodiments the substrate surface onwhich the rhenium-containing thin film or material is to be depositeddoes not comprise a semiconductor material, such as Si, Ge, III-Vcompounds, for example GaAs and InGaAs, or II-VI compounds. In someembodiments the substrate surface on which the rhenium-containing thinfilm or material is to be deposited may comprise materials other thaninsulating materials or may consist only of materials other thaninsulating materials.

Vapor deposition processes for depositing the rhenium-containing filmstypically involve the sequential provision of two or more reactants, forexample in an ALD- or CVD-type process. ALD type processes are based oncontrolled, typically self-limiting surface reactions of the precursorchemicals. Gas phase reactions are avoided by feeding the precursorsalternately and sequentially into the reaction chamber. Vapor phasereactants are separated from each other in the reaction chamber, forexample, by removing excess reactants and/or reactant by-products fromthe reaction chamber between reactant pulses. This may be accomplishedwith an evacuation step and/or with an inactive gas pulse or purge.

CVD type processes typically involve gas phase reactions between two ormore reactants. The reactants can be provided simultaneously to thereaction space or substrate, or in partially or completely separatedpulses. The substrate and/or reaction space can be heated to promote thereaction between the gaseous reactants. In some embodiments thereactants are provided until a thin film having a desired thickness isdeposited. In some embodiments cyclical CVD type processes can be usedwith multiple cycles to deposit a thin film having a desired thickness.In cyclical CVD-type processes, the reactants may be provided to thereaction chamber in pulses that do not overlap, or that partially orcompletely overlap.

In some embodiments a deposition process for a rhenium-containing thinfilm has one or more steps which are not self-limiting. For example, insome embodiments at least one of the reactants is at least partiallydecomposed on the substrate surface. Thus, in some embodiments theprocess may operate in a process condition regime close to CVDconditions or in some cases fully in CVD conditions. In some embodimentsa sequential or pulsed CVD process is utilized. In some embodiments amaterial comprising rhenium is deposited by a pulsed CVD process inwhich multiple pulses of a rhenium precursor and one or more additionalreactants are separated by purge or removal steps in which reactant isremoved from the substrate surface.

In some embodiments an ALD-process can be modified to be at least apartial CVD process. In some embodiments a partial CVD process caninclude at least partial decomposition of one or more precursors and/orat least partial overlap of two or more reactants. In some embodimentsALD processes can be modified to be a sequential or pulsed CVD process.A sequential or pulsed CVD process may utilize the same precursors andreaction conditions such as temperature and pressure as a correspondingALD process.

In some embodiments an ALD process is modified to use overlapping orpartially overlapping pulses of reactants. In some embodiments an ALDprocess is modified to use extremely short purge or removal times, suchas below 0.1 s (depending on the reactor). In some embodiments an ALDprocess is modified to use extremely long or continuous pulse times. Forexample, in some embodiments an ALD process is modified to use no purgeor removal at all after at least one reactant pulse. In some embodimentsno purge is used after a rhenium precursor pulse. In some embodiments nopurge is used after a second reactant pulse. In some embodiments nopurge is used after either a rhenium precursor pulse or a secondprecursor pulse.

Briefly, the substrate on which a rhenium-containing film is to bedeposited is loaded in a reaction chamber and is heated to a suitabledeposition temperature, generally at lowered pressure. For ALD-typeprocesses, deposition temperatures are maintained below the precursorthermal decomposition temperature but at a high enough level to avoidcondensation of reactants and to provide the activation energy for thedesired surface reactions. Of course, the appropriate temperature windowfor any given deposition process will depend upon a variety of factorsincluding the surface on which the rhenium-containing film is depositedand the reactant species involved. In some embodiments the depositiontemperature is below about 500° C. or below about 450° C., as discussedin more detail below.

In some embodiments, such as some CVD-type processes, the depositiontemperature may be above the decomposition temperature of one or more ofthe reactants. In some embodiments the deposition temperature is abovethe decomposition temperature of the rhenium precursor but still lowenough to maintain reasonably surface-controlled growth of a film. Forexample, in some such embodiments the growth rate of therhenium-containing film is less than or equal to about a monolayer ofmaterial per deposition cycle. In some embodiments a deposition cyclegrowth rate may be less than or equal to about 50%, preferably less thanabout 25%, and more preferably less than about 10% of about a monolayerof material being deposited per cycle.

In some embodiments a rhenium precursor may be contacted with thesubstrate intermittently while a second precursor may flow continuouslyor substantially continuously through a reaction space throughout adeposition process. For example, the flow rate of a second precursorthrough a reaction space may be reduced while the substrate is contactedwith a rhenium precursor. In some embodiments where a second precursormay flow continuously, the growth rate of the film per pulse of rheniumprecursor is less than or equal to about one monolayer of the materialbeing deposited. In some embodiments where the second precursor flowscontinuously, the growth rate per pulse of rhenium precursor is lessthan or equal to about 50%, preferably less than about 25%, and morepreferably less than about 10% of a monolayer of the material beingdeposited.

In some embodiments of an ALD-type process, the surface of the substrateis contacted with a vapor phase first rhenium precursor. In someembodiments a pulse of vapor phase first rhenium precursor is providedto a reaction space containing the substrate. In some embodiments thesubstrate is moved to a reaction space containing vapor phase firstrhenium precursor. Conditions are preferably selected such that no morethan about one monolayer of species of the first rhenium precursor isadsorbed on the substrate surface in a self-limiting manner. Theappropriate contacting times can be readily determined by the skilledartisan based on the particular circumstances. Excess first reactant andreaction byproducts, if any, are removed from the substrate surface,such as by purging with an inert gas or by removing the substrate fromthe presence of the first reactant.

Removing excess reactants can include evacuating some of the contents ofa reaction space and/or purging a reaction space with helium, nitrogenor another inert gas. In some embodiments purging can comprise turningoff the flow of the reactive gas while continuing to flow an inertcarrier gas to the reaction space.

Purging means that vapor phase precursors and/or vapor phase byproductsare removed from the substrate surface such as by evacuating thereaction chamber with a vacuum pump and/or by replacing the gas inside areaction chamber with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, and can be about 0.2and 10, or between about 0.5 and 5 seconds. However, other purge timescan be utilized if necessary, such as where highly conformal stepcoverage over extremely high aspect ratio structures or other structureswith complex surface morphology is needed, or where different reactortypes may be used, such as a batch reactor.

The surface of the substrate is subsequently contacted with a vaporphase second gaseous reactant. The second reactant reacts with therhenium-containing species from the first reactant adsorbed on thesubstrate to form the rhenium-containing material.

In some embodiments a pulse of a second gaseous reactant is provided toa reaction space containing the substrate. The vapor phase secondgaseous reactant may be provided into the reaction chamber in asubstantially continuous flow from a reaction chamber inlet to anoutlet. In some embodiments outlet flow from the reaction chamber, forexample a pump line, is not closed. In some embodiments outlet flow fromthe reaction chamber, for example flow from a reaction chamber to a pumpline and further through the pump line prior to the pump, is notsubstantially closed, but may be restricted. In some embodiments thesubstrate is moved to a reaction space containing the vapor phase secondreactant. After a desired period of exposure the substrate may be movedfrom the space containing the reactant.

Excess second reactant and gaseous byproducts of the surface reaction,if any, are removed from the substrate surface. In some embodimentsthere is no dwell time for the reactants.

The steps of contacting and removing form a deposition cycle that isrepeated until a rhenium containing thin film of the desired compositionand thickness has been selectively formed on the substrate, with eachcycle typically leaving no more than about a molecular monolayer ofrhenium-containing material.

The steps of contacting and removing a first vapor phase rheniumprecursor may be referred to as a first precursor phase, a rheniumprecursor phase, or a rhenium phase. The steps of contacting andremoving a second vapor phase reactant may be referred to as a secondprecursor phase or second reactant phase. Together, these two phases canmake up a deposition cycle. Additional phases comprising alternately andsequentially contacting the surface of a substrate with other reactantscan be included to form more complicated materials, such as ternarymaterials.

As mentioned above, each phase of each ALD cycle can be self-limiting.An excess of reactant precursors is supplied in each phase to saturatethe susceptible structure surfaces. Surface saturation ensures reactantoccupation of most or all available reactive sites (subject, forexample, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage and uniformity. Typically, less than onemolecular layer of material is deposited with each cycle, however, insome embodiments more than one molecular layer is deposited during eachcycle.

The precursors employed in the deposition processes may be solid, liquidor gaseous materials under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore they are contacted with the substrate surface. Contacting asubstrate surface with a vaporized precursor means that the precursorvapor is in contact with the substrate surface for a limited period oftime. Typically contacting times are from about 0.05 to 20 seconds, morepreferably between about 0.2 and 10, and still more preferably betweenabout 0.5 and 5 seconds. In some embodiments the contacting time isabout 1 second. In some embodiments the vapor phase second reactantcontacting time is preferably of the same order of magnitude as thevapor phase first gaseous reactant contacting time. In some embodimentsthe second reactant contacting time is less than about 60 seconds,preferably less than about 30 seconds, more preferably less than about10 seconds and most preferably less than about 5 seconds. In someembodiments the vapor phase second gaseous reactant contacting time ispreferably no more than about 100 times longer than the vapor phasefirst gaseous reactant contacting time.

However, depending on the substrate type and its surface area, thecontacting time may be even higher than 20 seconds. Contacting times canbe on the order of minutes or longer in some cases. The contacting timecan be determined by the skilled artisan based on the particularcircumstances.

The mass flow rate of the reactants can also be determined by theskilled artisan. In some embodiments the flow rate of a rheniumprecursor is preferably between about 1 and 1000 sccm withoutlimitation, or between about 100 and 500 sccm.

The pressure in a reaction chamber during the deposition of therhenium-containing thin film is typically from about 0.01 to about 50mbar, or from about 0.1 to about 10 mbar. However, in some cases thepressure will be higher or lower than this range, as can be determinedby the skilled artisan given the particular circumstances.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable deposition temperature. The deposition temperaturevaries depending on the type of thin film formed, physical properties ofthe precursors, etc. In some embodiments the deposition temperature isabout 20° C. to about 1200° C., about 50° C. to about 800° C., or about100° C. to about 600° C. In some embodiments the deposition temperatureis greater than about 50° C., greater than about 100° C., greater thanabout 200° C., greater than about 300° C., greater than about 400° C.,greater than about 500° C., or greater than about 600° C., but nogreater than 1200° C. In some embodiments the deposition temperature isabout 300° C. to about 500° C. In some embodiments the depositiontemperature is about 300 to about 400° C. In some embodiments thedeposition temperature is about 300° C. to about 450° C.

As mentioned above, in some embodiments each reaction is self-limitingand monolayer by monolayer growth is achieved. These may be referred toas “true ALD” reactions. In some such embodiments the rhenium precursormay adsorb on the substrate surface in a self-limiting manner. A secondreactant in turn will react with the adsorbed rhenium precursor to formup to a monolayer of rhenium0containing material on the substrate.

However, in some embodiments ALD-type reactions are provided, in whichthere may be some precursor decomposition, but the growth saturates.That is, in some embodiments although a certain amount of film growthmay be caused by thermal decomposition of the rhenium precursor at somedeposition temperatures, saturated growth is preferably achieved whenthe second reactant is utilized. Such a reaction is an example of anALD-type reaction. In such ALD-type reactions, films with gooduniformity and relatively few impurities can be deposited.

In some embodiments thermal decomposition of one or more reactantsoccurs, such as the rhenium precursor. In such cases, the growth ratemay not fully plateau with increasing reactant pulse times. Rather, thegrowth rate may continue to rise with increased pulse times, althoughthe growth rate may increase more slowly with ever increasing pulsetimes. Thus in some embodiments a pulsed-CVD type deposition process isused, in which reactants are provided alternately and separately, butsome gas-phase reactions may occur. Preferably the conditions areselected such that surface controlled decomposition is the mechanism fordecomposition, which leads to good uniformity and good step coverage.Reaction conditions can also be selected such that good control of thereactions is maintained, leading to good quality films with lowimpurities.

Thus, in some embodiments the deposition temperature is below thethermal decomposition temperature of the rhenium precursor (or otherreactant as described herein) while in other embodiments the depositiontemperature may be at or above the thermal decomposition temperature.

As mentioned above, in some embodiments a thin rhenium-containing filmis deposited on a substrate surface by a pulsed-CVD process in which avapor phase rhenium precursor is intermittently pulsed into a reactionspace comprising the substrate and purged from the reaction space. Thesubstrate may be contacted with a second vapor phase precursor, forexample in a sequential pulse. The pulses of the rhenium precursor andsecond precursor may at least partially overlap.

In some embodiments the deposited rhenium-containing thin film may besubjected to optional post deposition treatment process. In someembodiments, for example, a post deposition treatment process maycomprise an annealing process, for example a forming gas annealingprocess. In some embodiments a post deposition treatment process maycomprise exposing the rhenium-containing thin film to a plasma. In someother embodiments a post deposition treatment process does not compriseexposing the rhenium-containing thin film to a plasma.

The processing time depends on the thickness of the layer to be producedand the growth rate of the film. In ALD type processes, the growth rateof a thin film is determined as thickness increase per one cycle. Onecycle consists of the pulsing and purging steps of the precursors andthe duration of one cycle is typically between about 0.2 and 30 seconds,more preferably between about 1 and 10 seconds, but it can be on orderof minutes or more in some cases.

In some embodiments the deposition process is repeated to deposit arhenium containing film having a thickness of less than about 10molecular layers. In some embodiments the deposition process is repeatedto deposit a rhenium containing film having a thickness of less thanabout 5 molecular layers. In some embodiments the deposition process isrepeated to deposit a rhenium containing film having a thickness of lessthan about 3 molecular layers.

In some embodiments a rhenium-containing film is deposited to have athickness of less than about 10 nm, or less than about 5 nm.

Examples of suitable reactors that may be used for the deposition ofrhenium-containing thin films include commercially available ALDequipment such as the F-120® reactor, Pulsar® reactor and EmerALD™reactor, available from ASM America, Inc of Phoenix, Ariz. In additionto these ALD reactors, many other kinds of reactors capable ofdeposition of thin films, including CVD reactors equipped withappropriate equipment and means for pulsing the precursors, can beemployed for carrying out various embodiments disclosed herein.Preferably, reactants are kept separate until reaching the reactionchamber, such that shared lines for the precursors are minimized.

In some embodiments a suitable reactor may be a batch reactor and maycontain more than about 25 substrates, more than about 50 substrates ormore than about 100 substrates. In some embodiments a suitable reactormay be a mini-batch reactor and may contain from about 2 to about 20substrates, from about 3 to about 15 substrates or from about 4 to about10 substrates.

The growth processes can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, which clearlyimproves the throughput compared to a reactor in which is the substrateis heated up to the process temperature before each run.

Deposition of Thin Films Comprising Rhenium

As discussed above, thin films formed of rhenium-containing materialsmay be deposited by vapor deposition processes in which the substrate iscontacted with a rhenium reactant and a second reactant. In someembodiments the substrate is sequentially contacted with the reactants,such as in an ALD or pulsed-CVD process. The reactants and reactionconditions can be selected to deposit metallic rhenium, rhenium oxide,rhenium nitride, rhenium sulfide and mixtures thereof. As discussed inmore detail below, in some embodiments metallic rhenium, rhenium nitrideand mixtures thereof can be deposited using a rhenium precursor and anitrogen reactant. In some embodiments rhenium sulfide thin films can bedeposited using a rhenium precursor and a sulfur reactant.

More generally, according to some embodiments, and illustrated in FIG.1, a rhenium-containing thin film is formed on a substrate by anALD-type process comprising at least one deposition cycle 10 thedeposition cycle comprising:

contacting the surface of a substrate with a vaporized rhenium precursorat step 20 to form at most a molecular monolayer of rhenium-containingspecies on the substrate;

removing excess rhenium precursor and reaction by products, if any, fromthe surface at step 30;

contacting the surface of the substrate with a vaporized second reactantat step 40, such that the second reactant reacts with therhenium-containing species on the substrate surface to form arhenium-containing material; and

removing from the surface excess second reactant and any gaseousby-products formed in the reaction between the rhenium species and thesecond reactant at step 50.

The contacting and removing steps can be repeated 60 until arhenium-containing thin film of the desired thickness has been formed.

Although the illustrated deposition cycle begins with contacting thesurface of the substrate with the rhenium precursor, in otherembodiments the deposition cycle may begin with contacting the surfaceof the substrate with the second reactant. It will be understood by theskilled artisan that if the surface of the substrate is contacted with afirst reactant and that reactant does not react then the process willeffectively begin when the next reactant is provided.

In some embodiments, the reactants and reaction by-products can beremoved from the substrate surface by stopping the flow of the reactantwhile continuing the flow of an inert carrier gas such as nitrogen orargon. However, in some embodiments the substrate is moved such thatdifferent reactants alternately and sequentially contact the surface ofthe substrate in a desired sequence for a desired time. In someembodiments the removing steps are not performed. In some embodiments noreactant is removed from the various parts of a reaction chamber. Insome embodiments the substrate is moved from a part of a reactor orreaction chamber containing a first reactant or precursor to anotherpart of the reactor or reaction chamber containing the second reactant.In some embodiments the substrate is moved from a first reaction chambercontaining a first reactant to a second, different reaction chambercontaining a second reactant.

In some embodiments the rhenium-containing film may contain one or moreimpurities, such as C, H, O or Cl. In some embodiments the film maycontain less than about 3 at-% carbon, preferably less than about 2 at-%carbon, and most preferably less than about 1 at-% carbon. In someembodiments the film may contain 0.5 at-% carbon or less, 0.3 at-%carbon or less or even 0.1 at-% carbon or less. In some embodiments thefilm may contain less than about 12 at-% hydrogen, less than about 3at-% hydrogen, preferably less than about 2 at-% hydrogen, and mostpreferably less than about 1 at-% hydrogen. In some embodiments the filmmay contain about 0.6 at-% hydrogen or less, about 0.4 at-% hydrogen orless, about 0.3 at-% hydrogen or less, or about 0.2 at-% hydrogen orless. In some embodiments the film may contain less than about 60 at-%oxygen, less than about 20 at-% oxygen, less than about 10 at-% oxygen,or less than about 5 at-% oxygen. In some embodiments the film maycontain 2 at-% or less oxygen, 1 at-% or less oxygen, 0.6 at-% or lessoxygen, or 0.2 at-% or less oxygen. In some embodiments the film maycontain less than about 20 at-% Cl, less than about 10 at-% Cl, lessthan about 5 at-% Cl, less than about 2 at-% Cl, or less than about 1at-% Cl. In some embodiments the film may contain about 0.6 at-% Cl orless, or about 0.3 at-% Cl or less. It is to be noted that a rheniumcontaining film containing the above described impurities may still besuitable for different applications, such as for a 2D-material.

Suitable rhenium precursors may be selected by the skilled artisan. Insome embodiments the rhenium precursor is a rhenium halide. In someembodiments the rhenium halide comprises chloride. In some embodimentsthe rhenium precursor is ReCl₅. In some embodiments the rheniumprecursor comprises chlorine or a chloride ligand. In some embodimentsthe rhenium precursor is a rhenium fluoride, such as ReF₆. In someembodiments the rhenium precursor is a rhenium bromide. In someembodiments the rhenium precursor is a rhenium iodide.

As mentioned above, the rhenium precursor employed in the depositionprocesses may be solid, liquid or gaseous material, provided that therhenium precursor is in vapor phase before it is conducted into thereaction chamber and contacted with the substrate surface.

It will be understood by one skilled in the art that any number ofsecond reactants may be used in the vapor deposition processes disclosedherein, depending on the desired rhenium-containing film to bedeposited. In some embodiments the second reactant comprises at leastone hydrogen atom. In some embodiments a second reactant may be anitrogen precursor, or nitrogen containing reactant, such as NH₃. Insome embodiments a second reactant may be a sulfur reactant, such asH₂S. In some embodiments the second reactant does not comprise oxygen.In some embodiments the second reactant does not significantlycontribute material to the deposited material or the final formed film.In some embodiments the second reactant does contribute material to therhenium-containing film. For example, the nitrogen reactant maycontribute nitrogen to a rhenium nitride film or a film comprisingrhenium and rhenium nitride. Similarly, a sulfur reactant may contributesulfur to a rhenium sulfide film.

In some embodiments a nitrogen reactant may comprise nitrogen and atleast one hydrogen. In some embodiments a nitrogen reactant maycomprise, for example, N₂, NO₂, NH₃, N₂H₄ and/or other nitrogencontaining compounds.

In some embodiments, a sulfur reactant is utilized. In some embodimentsa sulfur reactant may be, for example, H₂S, an alkylsulfur compound suchas (CH₃)₂S, (NH₄)₂S, dimethylsulfoxide ((CH₃)₂SO), elemental or atomicS, or H₂S₂ or other reactants with the formula R—S—H, wherein R can be asubstituted or unsubstituted hydrocarbon, preferably a C1-C8 alkyl orsubstituted alkyl, such as an alkylsilyl group, more preferably a linearor branched C1-C5 alkyl group. In some embodiments, a sulfur precursorcomprises H₂Sn, wherein n is from 4 to 10.

In some embodiments the process may be a thermal process that does notutilize any plasma reactants. In some embodiments the process mayutilize a plasma. For example, nitrogen, hydrogen, sulfur or oxygencontaining plasma, radicals, excited species or atoms may be used in aplasma process. Plasmas may comprise a noble gas such as Ar or He, orcombinations of two or more noble gases. Plasmas may also comprisemixtures thereof, such as nitrogen and hydrogen containing plasma aswell as noble gas. For example, in some embodiments the plasma may begenerated in a mixture of N, H and noble gas.

2D Materials

The vapor deposition processes described herein may be used to deposit2D materials comprising rhenium, for example ReS₂ 2D materials. 2Dmaterials, also referred to as single layer materials, are materialsthat consist of a single connected molecular monolayer. While 2Dmaterials form a single connected molecular monolayer, multiplemonolayers may be deposited by the deposition processes disclosedherein. For example, in the case of 2D ReS₂, the 2D material comprises asingle layer of covalently bonded ReS₂ molecules, arranged so that onelayer of Re atoms is sandwiched between two layers of S atoms. However,ReS₂ can act as a 2D layer with thicker layers as well. Thus, asmentioned above, multiple monolayers may be deposited to form the 2Dmaterial.

Due to their unusual characteristics, 2D rhenium-containing materialsare useful in a wide variety of applications, for example aslubrication, in optoelectronics, spintronics and valleytronics, in THzgeneration and detection, for use as catalysts, chemical and biologicalsensors, supercapacitors, LEDs, solar cells, Li-ion batteries, and asMOSFET channel materials.

2D rhenium-containing thin films deposited by the methods disclosedherein possess electronic properties that make them useful forsemiconductor device miniaturization. For example, 2D rhenium sulfidefilms have a direct band gap and can be used as a channel material in agate stack or transistors.

According to some embodiments a 2D material comprising rhenium can bedeposited by vapor deposition according to the methods disclosed herein.In some embodiments a 2D material comprising rhenium may comprise lessthan or equal to ten molecular monolayers of a compound comprisingrhenium, less than or equal to five molecular monolayers, or less thanor equal to three molecular monolayers.

In some embodiments a method for depositing a 2D material comprisingrhenium on a substrate may comprise a deposition process as disclosedherein comprising at least one but less than or equal to 1000depositions cycles, less than or equal to 500 deposition cycles, lessthan or equal to 200 deposition cycles, or less than or equal to 100deposition cycles.

As can be selected by the skilled artisan depending on the particularprecursors, substrate and process conditions, a method for depositing a2D material comprising rhenium on a substrate may comprise an ALDprocess as disclosed herein comprising at least one but less than orequal to 1000 depositions cycles, less than or equal to 500 depositioncycles, less than or equal to 200 deposition cycles, or less than orequal to 100 deposition cycles, less than or equal to 50 cycles, lessthan or equal to 25 cycles, less than or equal to 15 cycles, or lessthan or equal to 10 cycles. In some embodiments the ALD cycle comprisesalternately and sequentially contacting the substrate with a rheniumprecursor and a second reactant as described herein.

In some embodiments the deposited 2D material comprising rhenium may be100 nm or less, 50 nm or less, 25 nm or less, 10 nm or less, 5 nm orless, 3 nm or less, 2 nm or less, 1.5 nm or less, or 1.0 nm or less,down to a single molecular layer or even a partial molecular layer.

Metallic Rhenium Thin Films

According to some embodiments, a metallic rhenium thin film is depositedon a surface of a substrate by a vapor deposition process comprising oneor more deposition cycles in which a substrate is sequentially contactedwith a vapor-phase rhenium precursor and a vapor phase second reactant.In some embodiments the vapor deposition process may be a cyclicaldeposition process in which the substrate is repeatedly contacted withtwo or more vapor phase reactants, for example, an atomic layerdeposition (ALD) process, a sequential chemical vapor deposition (CVD)process or a pulsed CVD process. In some embodiments a deposition cycleis repeated two or more times to form a metallic rhenium film of adesired thickness.

In some embodiments the vapor deposition process is an ALD-type processin which a substrate is alternately and sequentially contacted with avapor-phase rhenium precursor and a vapor phase second reactant. In someembodiments an ALD process comprises one or more deposition cycles, eachcycle comprising: pulsing a vaporized rhenium precursor into a reactionchamber where it contacts a substrate and forms up to a molecular layerof rhenium precursor species on a first surface of the substrate,removing excess rhenium precursor and reaction by products, if any, fromthe reaction chamber; providing a pulse of a second reactant, such asammonia containing gas into the reaction chamber to contact the firstsurface of the substrate, wherein the second reactant reacts with therhenium species on the surface to form a metallic rhenium material,removing excess second reactant and any gaseous by-products formed inthe reaction between the rhenium precursor species on the first surfaceof the substrate and the second reactant, and repeating the depositioncycle until a metallic rhenium thin film of the desired thickness hasbeen formed. In some embodiments the deposition cycle is repeated two ormore times.

In some embodiments the metallic rhenium film is elemental rhenium. Insuch embodiments the metallic rhenium thin film typically comprisesmultiple monolayers of elemental rhenium. However, in other embodiments,the thin film may comprise rhenium compounds or alloys comprisingrhenium and one or more different metals. In some embodiments theadditional materials may be provided by contacting the substrate withone or more additional reactants.

The rhenium precursor may be as described above. In some embodiments therhenium precursor may comprise rhenium and a halogen. Therhenium-containing precursor may be a rhenium halide precursor. In someembodiments, the rhenium precursor may comprise rhenium and one or morehalide, such as chloride ligands. In some embodiments the rheniumreactant may comprise one or more Re—Cl bonds. For example, in someembodiments the rhenium precursor may be ReCl₅. In some embodiments therhenium precursor may be a rhenium fluoride, such as ReF₆, a rheniumbromide or a rhenium iodide.

The second reactant is one that is able to react with the rheniumspecies on the substrate to form the desired metallic rhenium materialunder the selected deposition conditions. In some embodiments the secondreactant may be a nitrogen precursor, or nitrogen containing reactant.In some embodiments the second reactant may not significantly contributematerial to the final formed film. In some embodiments the secondreactant does contribute material to the rhenium-containing film.

In some embodiments the second reactant is a nitrogen precursor asdescribed above, for example, N₂H₄, N₂, NO₂, NH₃, and/or other nitrogencontaining compounds. However, in some embodiments the metallic rheniumthin film is not a rhenium nitride thin film.

In some embodiments the second reactant comprises hydrogen species. Insome embodiments the second reactant comprises one or more reactivespecies formed by generating a plasma in a reactant gas, as describedabove. For example, the plasma may be generated in H₂, or a gas mixturecomprising a noble gas. In some embodiments the second reactant does notcomprise molecular hydrogen in the absence of the formation of a plasma.

In some embodiments a film comprising rhenium, such as a metallic filmcomprising rhenium, is deposited at a deposition temperature of lessthan about 450° C. In some embodiments the deposition temperature isabout 120° C. to about 500° C., or about 250° C. to about 500° C. Insome embodiments the deposition temperature is about 20° C. to about1200° C., about 50° C. to about 800° C., or about 100° C. to about 600°C. In some embodiments the deposition temperature is greater than about50° C., greater than about 100° C., greater than about 200° C., greaterthan about 300° C., greater than about 400° C., greater than about 500°C., or greater than about 600° C., but no greater than 1200° C. In someembodiments the deposition temperature is about 300° C. to about 500° C.In some embodiments the deposition temperature is about 300 to about400° C. In some embodiments the deposition temperature is about 300° C.to about 450° C.

In some embodiments a metallic rhenium thin film is deposited at agrowth rate of about 0.01 Å/cycle to about 5 Å/cycle, from about 0.1Å/cycle to about 2 Å/cycle, or from about 0.2 Å/cycle to about 0.4Å/cycle. In some embodiments a metallic rhenium thin film is depositedat a growth rate of more than about 0.01 Å/cycle, 0.05 Å/cycle, 0.1Å/cycle, 0.2 Å/cycle, or 0.4 Å/cycle.

In some embodiments a method for depositing a metallic rhenium film on asubstrate may comprise from 1 to 1000 depositions cycles, from 1 to 500deposition cycles, from 1 to 200 deposition cycles, from 1 to 100deposition cycles, from 1 to 50 cycles, from 1 to 25 cycles, from 1 to15 cycles, or from 1 to 10 cycles. In some embodiments the ALD cyclecomprises alternately and sequentially contacting the substrate with arhenium precursor and a second reactant as described above.

In some embodiments the metallic rhenium film may have a thickness of100 nm or less, 50 nm or less, 25 nm or less, 10 nm or less, 5 nm orless, 3 nm or less, 2 nm or less, 1.5 nm or less, or 1.0 nm or less,down to a single molecular layer or even a partial molecular layer.

The metallic rhenium thin films may be deposited on a three-dimensionalstructure. In some embodiments the step coverage of the rhenium thinfilm may be equal to or greater than about 50, about 80, about 90, about95, about 98 or about 99%.

In some embodiments a metallic rhenium film may comprise one or moreimpurities, such as Cl, H, O and C. In some embodiments the film maycontain less than about 3 at-% carbon, preferably less than about 2 at-%carbon, and most preferably less than about 1 at-% carbon. In someembodiments the film may contain 0.5 at-% carbon or less, 0.3 at-%carbon or less or even 0.1 at-% carbon or less.

In some embodiments the film may contain less than about 20 at-%hydrogen, preferably less than about 10 at-% hydrogen, and mostpreferably less than about 5 at-% hydrogen. In some embodiments the filmmay contain less than about 12 at-% hydrogen, less than about 3 at-%hydrogen, preferably less than about 2 at-% hydrogen, and mostpreferably less than about 1 at-% hydrogen. In some embodiments the filmmay contain about 0.6 at-% hydrogen or less, about 0.4 at-% hydrogen orless, about 0.3 at-% hydrogen or less, or about 0.2 at-% hydrogen orless.

In some embodiments the film may contain less than about 60 at-% oxygen,less than about 20 at-% oxygen, less than about 10 at-% oxygen, or lessthan about 5 at-% oxygen. In some embodiments the film may contain 2at-% or less oxygen, 1 at-% or less oxygen, 0.6 at-% or less oxygen, or0.2 at-% or less oxygen.

In some embodiments the film may contain less than about 20 at-% Cl,less than about 10 at-% Cl, less than about 5 at-% Cl, less than about 2at-% Cl, or less than about 1 at-% Cl. In some embodiments the film maycontain about 0.6 at-% Cl or less, or about 0.3 at-% Cl or less.

In some embodiments the elemental N:Re ratio is from about 0.01 to about1, or from about 0.01 to about 0.6.

In some embodiments a metallic rhenium film has a resistivity of about10 to about 500 microOhmcm, or about 15 to about 200 microOhmcm. In someembodiments a metallic rhenium film has a resistivity of less than about1000 microOhmcm, less than about 500 microOhmcm, less than about 200microOhmcm, less than about 100 microOhmcm, less than about 50microOhmcm, less than about 30 microOhmcm or less than about 25microOhmcm.

In some embodiments a metallic rhenium thin film can serve as a workfunction-setting layer in a gate stack. In some embodiments the metallicrhenium thin film can serve as a copper capping layer. In someembodiments the metallic rhenium thin film can serve as a contact metallayer.

Rhesium Sulfide Thin Films

In some embodiments a rhenium sulfide thin film, such as a rheniumdisulfide thin film, is deposited on a substrate by a vapor depositionprocess. The rhenium sulfide may be a two-dimensional material. In someembodiments the vapor deposition process may be a cyclical depositionprocess in which the substrate is repeatedly contacted with two or morevapor phase reactants, for example, an atomic layer deposition (ALD)process, a sequential chemical vapor deposition (CVD) process or apulsed CVD process.

The deposition process is continued until a rhenium sulfide film of adesired thickness is deposited. The actual thickness may be selecteddepending on the particular circumstances. In some embodiments, arhenium sulfide film is deposited to a thickness of less than about 10nm or less than about 5 nm. In some embodiments the rhenium sulfide filmmay have a thickness of 10 nm or less, 5 nm or less, 3 nm or less, 2 nmor less, 1.5 nm or less, or 1.0 nm or less, down to a single molecularlayer or even a partial molecular layer.

In some embodiments the deposition processes allows for deposition ofvery thin rhenium sulfide layers. In some embodiments ReS₂ is depositedto a thickness of less than bout 20 molecular layers, less than about 10molecular layers, less than about 5 molecular layers or less than about3 molecular layers, down to a partial molecular layer.

In some embodiments a method for depositing a rhenium sulfide film on asubstrate may comprise from 1 to 1000 depositions cycles, from 1 to 500deposition cycles, from 1 to 200 deposition cycles, from 1 to 100deposition cycles, from 1 to 50 cycles, from 1 to 25 cycles, from 1 to15 cycles, or from 1 to 10 cycles. In some embodiments the ALD cyclecomprises alternately and sequentially contacting the substrate with arhenium precursor and a sulfur reactant as described above.

The rhenium sulfide thin films may be deposited on a three-dimensionalstructure. In some embodiments the step coverage of the rhenium thinfilm may be equal to or greater than about 50, about 80, about 90, about95, about 98 or about 99%.

In some embodiments a substrate is contacted with a rhenium-containingreactant and a sulfur-containing reactant to deposit a rhenium sulfidefilm. In some embodiments a rhenium disulfide (ReS₂) thin film isdeposited.

In some embodiments the sulfur-containing reactant may compriseelemental sulfur.

In some embodiments the vapor deposition process is an ALD-type processin which a substrate is alternately and sequentially contacted with avapor-phase rhenium precursor and a vapor phase second reactant. Asillustrated in FIG. 2, in some embodiments an ALD process comprises oneor more deposition cycles 100, each cycle comprising: contacting asubstrate in a reaction chamber with a vaporized rhenium precursor 200to form a molecular layer of rhenium precursor species on a firstsurface of the substrate, removing excess rhenium precursor and reactionby products 300, if any, contacting the substrate surface with a second,sulfur-containing reactant 400, such as H₂S, whereby the second reactantreacts with the rhenium precursor species on the substrate surface toform rhenium disulfide; removing excess second reactant and any gaseousby-products formed in the reaction between the rhenium precursor specieson the surface of the substrate and the second reactant 500, andrepeating the cycle 600 until a rhenium disulfide thin film of thedesired thickness has been formed.

As mentioned above, the substrate can comprise various types ofmaterials. In some embodiments the substrate may comprises a number ofthin films with varying chemical and physical properties. Further, thesubstrate surface may have been patterned and may comprise structuressuch as nodes, vias and trenches.

In some embodiments the rhenium precursor may comprise rhenium and ahalide, as described above. The rhenium-containing reactant may be arhenium halide precursor. In some embodiments, the rhenium reactant maycomprise rhenium and one or more chloride ligands. In some embodimentsthe rhenium reactant may comprise one or more Re—Cl bonds. For example,in some embodiments the rhenium precursor may comprise ReCl₅. In someembodiments the rhenium precursor may comprise a rhenium fluoride, suchas ReF₆, a rhenium bromide or a rhenium iodide.

In some embodiments the sulfur-containing reactant may comprise hydrogenand sulfur, as described above. In some embodiments thesulfur-containing reactant may comprise an H—S bond. In some embodimentsthe sulfur-containing reactant may be H₂S.

In some embodiments a film comprising rhenium, such a rhenium sulfide,is deposited at a deposition temperature of less than about 400° C. Insome embodiments the deposition temperature is about 100° C. to about500° C., or about 120° C. to about 500° C. In some embodiments thedeposition temperature is about 150° C. to about 350° C. In someembodiments the deposition temperature is about 200 to about 350° C. Insome embodiments the deposition temperature is about 200° C. to about300° C. In some embodiments the deposition temperature is from about 20°C. to about 1000° C., from about 50 to about 750 C. In some embodimentsthe deposition temperature is less than about 1000 C, less than about750 C, less than about 600 C, less than about 500 C.

In some embodiments films comprising rhenium are deposited at a growthrate of about 0.2 to about 1.0 A cycle-1. In some embodiments a thinfilm comprising rhenium is deposited at a growth rate of about 0.01Å/cycle to about 5 Å/cycle, from about 0.1 Å/cycle to about 2 Å/cycle,or from about 0.2 Å/cycle to about 0.4 Å/cycle. In some embodiments athin film comprising rhenium is deposited at a growth rate of more thanabout 0.01 Å/cycle, 0.05 Å/cycle, 0.1 Å/cycle, 0.2 Å/cycle, or 0.4Å/cycle.

In some embodiments a rhenium sulfide thin film is deposited at a growthrate of about 0.2 to about 1.0 A cycle-1. In some embodiments therhenium sulfide thin film is deposited at a growth rate of about 0.01Å/cycle to about 5 Å/cycle, from about 0.1 Å/cycle to about 2 Å/cycle,or from about 0.2 Å/cycle to about 0.4 Å/cycle. In some embodiments arhenium sulfide thin film is deposited at a growth rate of more thanabout 0.01 Å/cycle, 0.05 Å/cycle, 0.1 Å/cycle, 0.2 Å/cycle, or 0.4Å/cycle.

In some embodiments a rhenium sulfide film may comprise one or moreimpurities, such as Cl, H, O and C. In some embodiments the film maycontain less than about 3 at-% carbon, preferably less than about 2 at-%carbon, and most preferably less than about 1 at-% carbon. In someembodiments the film may contain less than about 20 at-% hydrogen,preferably less than about 10 at-% hydrogen, and most preferably lessthan about 5 at-% hydrogen. In some embodiments the film may containless than about 20 at-% oxygen, less than about 10 at-% oxygen, or lessthan about 5 at-% oxygen. In some embodiments the film may contain lessthan about 10 at-% Cl, less than about 5 at-% Cl or less than about 2at-% Cl.

In some embodiments the elemental S:Re ratio is from about 0.5 to about3, from about 1 to about 2.5, from about 1.5 to about 2.3, from about1.8 to about 2.2 or from about 1.9 to about 2.1. In some embodiments theelemental S:Re ratio is from about 0.8 to about 1.9.

In some embodiments the rhenium sulfide thin film can find use inintegrated circuits, semiconductor devices or optical devices. In someembodiments the rhenium sulfide film is used as a channel material in anintegrated circuit device, for example as a high mobility channelmaterial in a logic device. In some embodiments a 2D material is used inapplications where ultrathin, continuous and possibly pin-hole free tinfilms are utilized, such as in applications where electricallyconductive or semiconducting thin films are desired.

EXAMPLES

Thin rhenium-containing films were grown in a commercial cross-flowF-120 ALD reactor (ASM Microchemistry Ltd., Finland) under a nitrogenpressure of about 10 mbar. Nitrogen gas was provided from a liquidnitrogen tank and used as a carrier and a purging gas. In someexperiments deposition was on 5×5 cm2 substrates of Si(100) with nativeoxide on top or 5×5 cm2 substrates of soda lime glass. In someembodiments deposition was on Al2O3 films.

Crystal structures of the films were identified from X-ray diffraction(XRD) patterns measured with a PANalytical X'Pert Pro X-raydiffractometer in grazing incidence mode (GIXRD). Surface morphology ofthe films was examined by a Hitachi S-4800 field emission scanningelectron microscope (FESEM). Film thicknesses were determined fromenergy-dispersive X-ray spectroscopy (EDX) data measured using an OxfordINCA 350 microanalysis system connected to the FESEM. The EDX resultswere analyzed using a GMR electron probe thin film microanalysisprogram.

In some experiments, 20 nm thick rhenium metal films were grown at 400°C. on in-situ grown Al₂O₃ at a growth rate of 0.2 Å/cycle. The films hada resistivity of about 24 μΩcm.

Metallic Rhenium and Rhenium Nitride Deposition

Deposition of metallic rhenium was carried out using ReCl₅ and NH₃ asprecursors. ReCl₅ (99.9%-Re, Strem) was sublimed from an open boat heldinside the reactor at 110° C. and pulsed into the reaction chamber usinginert gas valving. The flow rates of H₂S (99.5%, Linde) and NH₃(99.9999%, Linde) were set to 10 sccm during continuous flows via massflow meters and needle valves. All of the precursor pulse lengths were 2s each while the purges were 1-2 s each.

FIG. 3 presents the GIXRD patterns obtained from deposition on Sisubstrates at deposition temperatures between 150 and 500° C. The filmsdeposited at between 300 and 500° C. were metallic in appearance, whiledeposition on substrates at lower deposition temperatures wasnon-uniform and dark in color. The films grown at 400 and 500° C. wereidentified to be metallic Re as shown in FIG. 3. In addition, someunidentifiable peaks were visible in the patterns at lower angles. Alsoin FESEM images some larger grains could be seen (FIG. 4), which mayhave been related to these unidentified peaks. The films deposited atdeposition temperatures of 300 and 400° C. revealed that part of thefilms were either delaminated from the Si surface (300° C.) or showedcracking patterns (400° C.) (FIG. 5).

The growth rates of the rhenium films at various deposition temperaturesare shown in FIG. 6. The growth rates were about 0.2-0.3 Å/cycle atdeposition temperatures between 300 and 500° C. Films deposited on anALD AlN surface had a slightly higher growth rate compared to the filmdeposited on a Si substrate at 300° C.

In other experiments rhenium films were deposited on an ALD-depositedaluminum oxide surface by ALD using ReCl₅ and NH₃ as reactants. The ALDprocess comprised multiple deposition cycles in which the substrate wascontacted with a pulse of ReCl₅, the reaction space was purged for afirst period of time, the substrate was contacted with a pulse of NH₃and the reaction space was purged for a second time. FIG. 7 illustratesthe growth of rhenium thin films as a function of ReCl₅ pulse length for1000 cycles of the ALD process at 400° C. The ReCl₅ pulse length wasvaried from 0.5 to 4 seconds, while the NH₃ pulse length was maintainedat 2 seconds. The purge length was 1 second. FIG. 8 shows the growthrate of the rhenium thin film when the NH₃ pulse length was varied from0.25 to 4 seconds and the ReCl₅ pulse length was maintained at 2seconds.

FIG. 9 illustrates the growth rate of the rhenium thin film on aluminumoxide as a function of NH₃ flow rate. The pulse length of precursors was2 seconds and the purge was 1 second. Again, a total of 1000 depositioncycles was carried out at a temperature of 400° C.

FIG. 10 shows the increase in rhenium thin film thickness as a functionof number of deposition cycles. As in the above experiments, depositionwas on aluminum oxide films at 400° C. using ReCl₅ and NH₃ pulses of 2seconds and purges of 1 second each.

FIG. 11 shows the growth rate of rhenium thin films on aluminum oxide asa function of deposition temperature, using reactant pulse lengths of 2second, and purge lengths of 1 second for 1000 deposition cycles.

FIG. 12 illustrates the growth rates and resistivities of rhenium thinfilms grown on Al₂O₃ films at 400° C. as a function of ReCl₅ pulselength using NH₃ as the second reactant. The pulse length of NH₃ was 2 sand all purges were 1 s. A total of 1000 deposition cycles was used.

FIG. 13 illustrates growth rates and resistivities of rhenium-containingthin films grown on Al₂O₃ at 400° C. as a function of NH₃ pulse length.The pulse length of ReCl₅ was 2 s and all purges were is each. A totalof 1000 deposition cycles was used.

FIG. 14 illustrates growth rate and resistivities of rhenium thin filmsgrown on Al₂O₃ at 400° C. as a function of NH₃ flow rate. The pulselengths of the precursors and purges were 2 s and is respectively. Atotal of 1000 deposition cycles was used.

FIG. 15 illustrates the thickness and resistivities of rhenium thinfilms grown on Al₂O₃ from ReCl₅ and NH₃ at 400° C. as a function of thenumber of deposition cycles. The pulse lengths of the precursors andpurges were 2 s and is each, respectively. FIG. 16 shows GIXRD patternsfor rhenium thin films grown on Al₂O₃ at 400° C. from ReCl₅ and NH₃ as afunction of number of deposition cycles. FIG. 17 shows FSEM images ofthe films.

Rhenium nitride and rhenium metal films were grown by ALD on Al₂O₃ usingReCl₅ and NH₃. FIG. 18 shows the growth rates and resistivities of thefilms as a function of deposition temperature. The pulse and purgelengths were is each, and a total of 1000 deposition cycles was used.FIG. 19 shows the GIXRD patterns of the rhenium nitride and rheniummetal films. FIG. 20 provides the film thickness and surface roughnessof the rhenium metal and rhenium nitride films deposited between 250° C.and 500° C. FIG. 21 provides AFM images (2 micron×2 micron) of therhenium metal and rhenium nitride films gown on Al₂O₃ as a function oftemperature.

FIG. 22 shows FESEM images of rhenium and rhenium nitride films grown onAl₂O₃ films at deposition temperatures between 250° C. and 500° C. in acommercial hot-wall flow-type F-120 ALD reactor (ASM MicrochemistryLtd). In-situ 5-10 nm Al₂O₃ coated 5×5 cm² Si(100) substrates were used.As in the above experiments, ReCl₅ and NH₃ pulses of 2 seconds andpurges of 1 second each were used. The total number of deposition cyclesat each temperature was 1000.

FIG. 23 shows the elemental composition, impurity content andstoichiometry of the rhenium metal/rhenium nitride films depositedbetween 250° C. and 500° C. as analyzed by TOF-ERDA. The Al₂O₃ film wasdetermined from the thinnest ReN_(x) sample structures, and the Al₂O₃layer was reduced from the samples by assuming the Al₂O₃ layer to beidentical in each case. Thus, the 0 content is indicative only.

Rhenium Sulfide Deposition

Rhenium sulfide was deposited by ALD using ReCl₅ and H₂S as precursors.FIG. 24 presents the GIXRD patterns obtained from films grown on Sisubstrates at deposition temperatures between 150 and 500° C. The filmsgrown between 200 and 500° C. could be identified as anorthic ReS₂(00-024-0922; unnamed mineral, syn [NR]), however the pattern has anumber of peaks. The highest intensity in the patterns is visible around14-15° and is ReS₂ (001), whereas the low intensity peak next to it andvisible at 300° C. is ReS₂ (100). The main peak visible at around 320 inthe films grown at 200 and 300° C. could belong to any of the ReS₂ (200)[32.113° ], (0-21) [32.364], (−220) [32.766], or (−201) [32.915] peaks.The film grown at 150° C. was nearly X-ray amorphous, though it reactedwith a plastic bag surface before the pattern was measured. The visiblereaction may have been related to the cracking of the film as seen inFIG. 25.

The growth rates of the rhenium sulfide thin films on Si substrates arepresented in FIG. 26. The film grown at 150° C. had a growth rate ofabout 0.8 Å/cycle whereas the growth rate increased to about 1.2 Å/cyclefor the film grown at 200° C. The growth rate decreased as thedeposition temperature increased, from 1.2 Å/cycle at 200° C. to around0.4 Å/cycle at 500° C. The surface morphologies of the films are shownin FIG. 27. Comparison between the starting surfaces of native oxidecovered Si and ALD grown Al2O3 did not reveal any difference for rheniumsulfide growth at 300° C. (FIGS. 28 and 29).

Rhenium sulfide was also deposited by ALD on ALD-grown Al₂O₃ films atvarious deposition temperatures from ReCl₅ and H₂S. The ALD processcomprised multiple deposition cycles in which the substrate wascontacted with a pulse of ReCl₅, the reaction space was purged for afirst period of time, the substrate was contacted with a pulse of H₂Sand the reaction space was purged for a second time. FIG. 30 illustratesthe growth rate of rhenium sulfide films on Al₂O₃ at 400° C. as afunction of ReCl₅ pulse length. The pulse length of H₂S was 2 secondswhile the purge lengths were 1 second each. A total of 1000 depositioncycles were carried out. FIG. 31 shows the growth rate of rheniumsulfide films on Al₂O₃ as a function of H₂S pulse length, with a ReCl₅pulse length of 1 second and purge lengths of 1 second. Again, a totalof 1000 deposition cycles were carried out at a deposition temperatureof 400° C. FIG. 32 shows FSEM images of the films deposited with thevarious H₂S pulse lengths.

FIG. 33 shows the increasing thickness of rhenium sulfide filmsdeposited on Al₂O₃ at 400° C. using 1 second pulses of ReCl₅ and H₂S,and 1 second purges. FIG. 36 provides the film thicknesses (calculatedby EDX) and surface roughness (calculated by AFM) for the rhenium filmsdeposited with varying number of deposition cycles. GXIRD patterns ofthese rhenium sulfide films are shown in FIG. 34 and FSEM images of therhenium sulfide films are shown in FIG. 35.

FIG. 37 shows the growth rate of rhenium sulfide films grown on Al₂O₃films as a function of deposition temperature. The pulse lengths for theReCl₅ and H₂S were 1 second and the purge lengths were also 1 secondeach, for a total of 1000 deposition cycles. GXIRD data for theserhenium sulfide films are shown in FIG. 38 and FSEM images of the filmsare shown in FIG. 39. FIG. 40 shows the elemental composition, impuritycontent and stoichiometry of the rhenium sulfide films deposited between120° C. and 500° C. as measured by TOF-ERDA. FIG. 41 shows the elementalcomposition, impurity content and stoichiometry of the same films asmeasured by XPS. At 120° C. and above, 80% of the rhenium is Re(IV).These films were deposited without optimization in a research reactor,and demonstrate that ReS films can be deposited. Further optimizationcan reduce the impurities and tune the composition as desired forparticular situations.

ReS₂ films were deposited on in-situ grown Al₂O₃ from ReCl₅ and H₂S byALD at deposition temperatures up to 500° C. An FESEM image of one ofthese ALD ReS₂ films is shown in FIG. 42. A TEM image of the same ALDReS₂ film is shown in FIG. 43. FSEM images of rhenium sulfide filmsdeposited in a trench structure are shown in FIGS. 44A-D.

What is claimed is:
 1. A method for depositing a thin film comprisingrhenium sulfide on a substrate, the method comprising two or moresequential deposition cycles each comprising alternately andsequentially contacting the substrate with a vapor-phase rheniumprecursor comprising a rhenium halide compound and a vapor-phase sulfurreactant.
 2. The method of claim 1, wherein the method is an atomiclayer deposition (ALD) process.
 3. The method of claim 1, wherein themethod is a sequential or pulsed chemical vapor deposition (CVD)process.
 4. The method of claim 1, wherein the vapor-phase rheniumprecursor comprises ReCl₅ or ReF₆.
 5. The method of claim 1, wherein thevapor-phase sulfur reactant comprises hydrogen and sulfur.
 6. The methodof claim 1, wherein the vapor-phase sulfur reactant is an alkylsulfurcompound.
 7. The method of claim 1, wherein the vapor-phase sulfurreactant comprises elemental sulfur.
 8. The method of claim 1, whereinthe vapor-phase sulfur reactant has the formula R—S—H, wherein R is asubstituted or unsubstituted hydrocarbon.
 9. The method of claim 8,wherein R is a C1-C8 alkyl or substituted alkyl
 10. The method of claim1, wherein the vapor-phase sulfur reactant comprises H₂S_(n), wherein nis from 4 to
 10. 11. The method of claim 1, wherein the vapor-phasesulfur reactant comprises one or more of H₂S, (CH₃)₂S, (NH₄)₂S,((CH₃)₂SO), and H₂S₂.
 12. The method of claim 1, wherein the vapor-phasesulfur reactant comprises (NH₄)₂S.
 13. The method of claim 1, whereinthe deposition cycles are carried out at a deposition temperature of 200to 350° C.
 14. The method of claim 1, wherein the rhenium sulfide thinfilm comprises ReS₂.
 15. The method of claim 1, wherein the rheniumsulfide thin film comprises ReS₂, the vapor-phase rhenium precursorcomprises ReCl₅ and the vapor-phase sulfur reactant comprises H₂S. 16.The method of claim 1, wherein the rhenium sulfide thin film comprises atwo-dimensional material.
 17. The method of claim 1, wherein the rheniumsulfide thin film serves as a high mobility channel material in a logicdevice.
 18. The method of claim 1, wherein the deposition cycles arerepeated sequentially to form 20 molecular layers of ReS₂ or less. 19.The method of claim 1, wherein the rhenium sulfide thin film has an S:Reratio from 0.5 to
 3. 20. The method of claim 1, wherein the rheniumsulfide thin film is deposited on a three-dimensional structure withstep coverage of greater than 90%.
 21. The method of claim 1, whereinthe rhenium sulfide thin film contains less than 20-at % hydrogen, lessthan 2 at-% carbon and less than 20 at-% oxygen.
 22. The method of claim1, wherein the rhenium sulfide thin film contains less than 10 at-% Cl.